Sections 9.7 and 9.8

Specific Heat Capacity and Thermal Expansion

Objectives

By the end of today, you will be able to:

define and explain specific heat capacity

define and explain thermal expansion

PS - F-11, 15, and 17

9.7 - Specific Heat Capacity

Different substances have different capacities for storing thermal energy.

When you heat a pot of water on a stove, it takes about 15 minutes to bring it to a boil

An equal amount of iron, it only takes about 2 minutes to raise it through the same temperature range

For silver, it would only take about a minute

9.7 - Specific Heat Capacity

As you can see, different materials require different amounts of thermal energy to raise temperature.

This is because different materials absorb energy in different ways.

This is called an object’s specific heat capacity -

The specific heat capacity of any substance is defined as the quantity of heat required to change the temperature of a unit mass (g or kg) of the substance by 1 degree

9.7 - Specific Heat Capacity

Consider the difference between touching an empty iron skillet that has been placed on a hot stove for one minute and touching the same skillet filled with water.

What would happen?

9.7 - Specific Heat Capacity

You could safely place your hand in the water filled skillet even if it were on the stove for several minutes!

Why?

Water has a very high specific heat capacity, and therefore, it requires much more thermal energy (heat) to change its temperature!

9.7 Specific Heat Capacity

Because of water’s high specific heat, it absorbs large amounts of heat for small changes in temperature. It also takes longer to cool.

In fact, this property of water changes the world’s climate.

Areas that are near, or are surrounded by, water have much smaller ranges in temperature

The water warms, or cools, the air as it blows over it, which, then, blows onto the land, thus affecting the temperature.

9.8 - Thermal Expansion

What is happening to the molecules in a hot substance?

They are moving faster and moving farther apart.

The result of this is called thermal expansion.

9.8 - Thermal Expansion

Most substances expand when heated and contract when cooled.

Liquids expand more than solids with increases in temperature.

These changes aren’t always noticeable ...

9.8 - Thermal Expansion

. . . . But sometimes they are!

9.8 - Thermal Expansion

Telephone wires are longer and sag more on hot summer days

Railroad Tracks can expand and buckle in the summer.

Pouring hot water over the lid of a jar that is difficult to open.

9.8 - Thermal Expansion

Thermal expansion must be taken into account when building structures and devices.

Like the expansion joints on a bridge

9.8 - Thermal Expansion

Water behaves a little differently than most substances.

Water initially (between 0° C and 4° C) expands when cooled and contracts when heated.

(This is due to the crystal structure of ice)

9.8 - Thermal Expansion

Vocabulary Quiz Terms

thermal energy, temperature, absolute zero, heat, joule, calorie, thermodynamics, specific heat capacity, thermal expansion